1. Field of the Invention
The present invention relates generally to an apparatus for controlling operation of an internal combustion engine (hereinafter also referred to simply as the engine) by controlling fuel injections, ignition timings and the like for the individual engine cylinders, respectively, on the basis of a reference position signal and a cylinder identification signal. More particularly, the invention is concerned with an engine control apparatus which can be applied to a multi-cylinder engine including a given number of cylinders and in which the reference positions for the individual cylinders can speedily be detected with high reliability.
2. Description of the Related Art
In general, in the multi-cylinder engine for an automobile or motor vehicle, it is required to control optimally the fuel injections and the ignition timings in dependence on the operation state of the engine or motor vehicle. To this end, there is provided a signal generating means inclusive of a sensor in association with a rotatable shaft of the engine for making available a reference position signal indicating reference positions for the individual engine cylinders and a cylinder identification signal for identifying a particular cylinder, respectively. Further, a microcomputer is used for detecting a reference crank angle position for each cylinder on the basis of the signals mentioned above and effectuating timer-based control operation on the basis of the reference positions for the cylinders by determining through calculation the control timings such as the ignition timings and the like.
FIG. 5 is a block diagram showing an engine control apparatus of the above-mentioned type known heretofore. Referring to the figure, this known engine control apparatus includes a reference position signal generating means 1 for generating a reference position signal T representing reference crank angle positions on a cylinder-by-cylinder basis in synchronism with rotation of a crank shaft of the engine (not shown) and a cylinder identification (ID) signal generating means 2 for generating a cylinder identification (ID) signal C for identifying a particular cylinder in synchronism with rotation of a shaft (e.g., a cam shaft) interlocked to the crank shaft and having a rotation frequency equal to a half of that of the crank shaft, and a variety of sensors (generally denoted by a reference numeral 3) for detecting the operation state of the engine such as a rotation speed (rpm) of the engine, loads thereof and others.
The reference position signal T, the cylinder identification signal C and the operation state signal D are inputted to a control means 4 which controls the engine on the basis of these signals and which includes a reference position determination unit 4 for deciding or determining the reference position for each engine cylinder on the basis of the reference position signal T and the cylinder identification signal C, and a timing determination unit 42 for generating a control signal for controlling the ignition timings or the like for the individual cylinders on the basis of the output signal F from the reference position determination unit 41 and the operation state signal D derived from the sensor set 3.
FIG. 6 is a perspective view showing typical structures of the reference position signal generating means 1 and the cylinder identification signal generating means 2, respectively. Referring to the figure, the reference position signal generating means 1 includes a signal disk 11 which is mounted on a crank shaft 10 and thus rotated in synchronism with the rotation of the engine and has twelve teeth or projections 12 of a magnetic material formed equidistantly along the outer peripheral edge of the disk 11, wherein an electromagnetic pick-up 13 is disposed in opposition to the array of the magnetic projections 13. The signal disk 11 with the magnetic projections 13 cooperates with the electromagnetic pick-up 13 to constitute the reference signal generating means 1.
On the other hand, the cylinder identification signal generating means 2 includes a cam shaft 20 which is operatively connected to the crank shaft 10 through a reduction gear train or the like transmission means so that the former is rotated at a speed (rpm) equal to a half of that of the latter. A second signal disk 21 is mounted on the cam shaft 20 for rotation therewith. This signal disk 21 has only one magnetic projection or tooth 22 formed on the outer peripheral edge thereof. A second electromagnetic pick-up 23 is disposed in opposition to a path along which the projection 22 rotates. The disk 21 having the projection 22 cooperates with the electromagnetic pick-up 23 to constitute the cylinder identification signal generating means 2.
FIG. 7 is a timing chart which illustrates the reference position signal T and the cylinder identification signal C together with the decision signal F on the assumption that the number of the engine cylinders to be controlled is four. As can be seen in this figure, the reference position signal T contains twelve pulses per rotation of the crank shaft 10 on the basis of which reference crank angle position signals representing, for example, a crank angle of B75.degree. (indicating a crank angle 75.degree. before the top dead center or TDC) and a crank angle of B15.degree. respectively, for each of the cylinders.
On the other hand, the cylinder identification signal C has a period of 720.degree. in terms of the crank angle for all the cylinders, because the cam shaft 20 rotates only once during a period in which the crank shaft 10 rotates twice. Thus, the inter-pulse intervals .theta..sub.2 of the reference position signal T is 30.degree. in terms of the crank angle.
Further, the cylinder identification signal C contains a single pulse generated once during the period of 720.degree. for a particular cylinder (cylinder #1 in the case of the illustrated example), which pulse has a phase difference .theta..sub.1 (e.g., about 15.degree.) relative to the pulse of the reference signal position signal T.
Next, description will turn to operation of the known engine control apparatus shown in FIG. 5 by reference to FIGS. 6 and 7.
When the engine rotates, the reference position signal generating means 1 and the cylinder identification signal generating means 2 generate the reference position signal T and the cylinder identification signal C which have waveforms such as illustrated in FIG. 7, respectively. These signals T and C are supplied to the reference position determination unit 41 of the control means 3.
The reference position determination unit 41 determines the position of the pulse contained in the reference position signal T which pulse lags to the generation of the pulse of the cylinder identification signal C by the crank angle .theta..sub.1 as the reference position B75.degree. for the cylinder #1. Subsequently, the reference position determination unit 41 decides the reference positions for the individual cylinders on the basis of the reference position signal pulses T generated at every crank angle .theta..sub.2 (=30.degree.), to thereby generate the reference position decision signals F each indicating the reference positions B75.degree. and B15.degree. for each of the other cylinders.
In the case of the engine including four cylinders, the reference position decision signals F each containing the pulse which indicates the reference positions B75.degree. and B15.degree., respectively, are successively generated for the cylinders #3, #4 and #2 in this sequence in succession to the generation of the reference position pulse signal for the cylinder #1 during a period corresponding to the crank angle of 720.degree..
Parenthetically, it should be mentioned that when the reference position signal generating means 1 which is configured to generate 24 pulses during a period corresponding to the crank angle of 720.degree. is employed as illustrated in FIGS. 6 and 7, the engine control under consideration can be applied not only to the four-cylinder engine but also to a three-cylinder engine, a six-cylinder engine, an eight-cylinder engine and a twelve-cylinder engine (these engines may collectively be referred to as the multicylinder engine).
The timing control unit 42 detects the reference positions for the individual cylinders on the basis of the reference position decision signal F to thereby calculate the control quantity for controlling the ignition timing or the like in dependence on the engine operation state D, as a result of which the control signals for controlling the ignition timings for the individual cylinders are outputted. In that case, when the ignition timing is to advance, the timing control (based on a timer control) is performed with reference to the reference position of B75.degree., while when the ignition timing is to lag, the timing control is then performed with reference to the second reference position of B15.degree..
At this juncture, it should be noted that the pulses of the reference position signal T and the cylinder identification signal C are inherently of very short duration (spike-like pulse) because they are generated by using the electromagnetic pick-up devices 13 and 23. For this reason, there is a possibility that some noise may erroneously be detected as the reference position signal pulse and/or as the cylinder identification signal pulse. Further, because the cylinder identification signal C contains only one pulse for identifying discriminatively to the cylinder #1 during a period corresponding to the crank angle of 720.degree., a lot of time which will amount to 720.degree. in the worst case will be required for detecting the reference positions for the individual cylinders.
As will be appreciated from the above description, the engine control apparatus known heretofore suffers from problems that the susceptibility to noise is high with the reliability of the reference position determination for the cylinder being degraded and that a lot of time is taken for detecting the reference positions for the individual cylinders.